Catálogo de publicaciones - libros

Future generation networks are expected to be a combination of several types of access technologies that vary in their characteristics. Efficient handoff management techniques are required to enable end-users to seamlessly access these networks as they roam across different geographic locations. We describe recent protocols (application, transport, and network) such as Mobile IP, Session Initiation Protocol (SIP), and Stream Control Transmission Protocol (SCTP) that have been deployed to handle handoffs. We present an empirical performance evaluation of the three protocols using performance metrics such as handoff delay. We found that Mobile IP yields the highest handoff delay out of all the three mobility protocols. SIP and SCTP yield (33 %) and (55 %) lower handoff delays compared to Mobile IP.

It is known that multicast is an efficient method of supporting group communication as it allows the transmission of the packets to multiple destinations using fewer network resources. Along with the widespread deployment of the third generation cellular networks and the fast-improving capabilities of the mobile devices, content and service providers are increasingly interested in supporting multicast communications over wireless networks and in particular over Universal Mobile Telecommunications System (UMTS). In this paper, a multicast scheme for UMTS is analyzed. We analytically present the multicast routing mechanism behind our scheme as well as the multicast group management functionality of the scheme. Furthermore, we present an evaluation of our scheme in terms of its performance. The critical parameters for the evaluation of the scheme are the number of users within the multicast group, the amount of data sent to the multicast users, the density of the multicast users within the cells and finally the type of transport channel used for the transmission of the multicast data over the air.

Many studies have been performed to improve the efficiency of mobile IP. Hierarchical MIPv6 (HMIPv6) was proposed due to the lack of MIPv6. The new protocol, that is, Mobility Anchor Point (MAP) receives all packets in place of Mobile Node (MN) and MAP services are transferred to Care of Address (CoA) of MN However, it can affect the whole network owing to concentration phase of registration occurred in hierarchical MAP structure. We propose the scheme that selects different MAP according to the traffic characteristic. The quantitative result and performance analysis presented in this paper show that our proposal can reduce the cost of location update by 5% and total cost of MN that moves frequently by 34%.

One of the most important challenges in cellular networks is to utilize the scarce spectrum allocated to the network in the most efficient way. If the channels are statically allocated to the cells, when a large number of mobile hosts move to the cell, that cell may run out of channels resulting in a high call incompletion rate. To overcome this problem, dynamic channel allocation schemes have been proposed. Among these schemes, distributed dynamic channel allocation approaches resulted in good performance results. Nevertheless, distributed allocation schemes must address the problem of efficient co-channel interference avoidance and reducing messaging overhead issues. In this paper, we introduced a new distributed channel allocation scheme namely the DonorList approach, which decreases the amount of messages required per channel allocation while efficiently handling the co-channel interference problem. We also demonstrate the performance results obtained after extensive simulation studies. The results show that the proposed algorithm outperforms the other algorithms recently proposed in the literature.

In recent years there has been an explosive growth on the use of wireless video communications. Despite much research in this field, the deployment of effective QoS-aware real-time video services over wireless channels remains a challenging task. In this paper, we first introduce and describe an overall system architecture capable of offering true end-to-end QoS guarantees to MPEG-4 video services running over TDMA/TDD wireless networks. The proposed system architecture is built by integrating two key system elements: a set of control mechanisms and various error resilient techniques. After reviewing the various system elements, we evaluate the use of the various mechanisms. We show the effectiveness of the proposed architecture in terms of various metrics. Our results show that the video quality as perceived by the end user can be significantly improved by making use of hierarchical video coding techniques.

In this paper, two different dynamic cell coordination stratagies for frequency selective and flat fading are proposed for efficient subcarrier allocation in the joint consideration of adaptive modulation and variable frequency reuse in the channel-aware OFDMA downlink multicellular environment. Compared to a conventional OFDMA system without cell coordination, where system throughput may become degraded due to the persistent interference from other cells, the proposed system dynamically allows RNC to apply different reuse factors on each subchannel and scheduling in consideration of channel and interference conditions of individual users so as to increase the system throughput and guarantee QoS of each user. In a selective fading channel, the proposed schemes showed 2.6 times as large throughput as that of a single reuse factor of one for all subcarriers. In a frequency flat fading, the dynamic scheme with the proposed scheduling achieves on average three times larger throughput than the conventional dynamic scheme [8].

In this paper we present a comparison among three different monitoring functions to be used in a dynamic bandwidth renegotiation scheme. These functions aim at detecting the amount of unused resources in the network, which can be allocated to low priority data flows. These applications are not delay-sensitive and can be admitted by the call admission control with a bandwidth smaller than the nominal one. Simulation results comparing the performance of the three monitoring functions are presented, as well as an overhead analysis. Finally, we discuss the performance/complexity trade-off considering the three functions and determine the most viable one.

In the few last years, the deployment of IEEE 802.11 WLAN in hotspots environment had becoming a useful solution providing practical and attractive communication characteristics. However the problem of user bandwidth availability arises as one of the most limit of this solution. In fact, the IEEE 802.11 standards do not provide any mechanism of load distribution among different access points (APs). Then an AP can be heavily overloaded leading to station throughput degradation. This paper deals with this problem. It focuses on the presentation of QoS (Quality of Service) management solution for wireless communication system. It, mainly, presents a protocol structure between mobiles and APs. This protocol is intended to provide best resources allocation and efficiency on communication metrics. An SDL description and MSC simulation is provided as a first step in the development of this protocol.

The main objective of clustering in mobile ad-hoc network environments is to identify suitable node representatives, i.e. cluster heads (CHs) to store routing and topology information; CHs should be elected so as to maximize clusters stability, that is to prevent frequent cluster re-structuring. A popular clustering algorithm (LID) suggests CH election based on node IDs (nodes with locally lowest ID value become CHs). Although fast and simple, this method is biased against nodes with low IDs, which are likely to serve as CHs for long periods and are therefore prone to rapid battery exhaustion. Herein, we propose LIDAR, a novel clustering method which represents a major improvement over traditional LID algorithm: node IDs are periodically re-assigned so that nodes with low mobility rate and high energy capacity are assigned low ID values and, therefore, are likely to serve as CHs. Our protocol also greatly reduces control traffic volume of existing algorithms during clustering maintenance phase, while not risking the energy availability of CHs. Simulation results demonstrate the efficiency, scalability and stability of our protocol against alternative approaches.

In wireless networks, devices must be able to dynamically discover and share services in the environment. The problem of service discovery has attracted great research interest in the last years, particularly for ad hoc networks. Recently, the IETF has proposed the use of the DNS protocol for service discovery. For ad hoc networks, the IETF works in two proposals of distributed DNS, Multicast DNS and LLMNR, that can both be used for service discovery. In this paper we describe and compare through simulation the performance of service discovery based in these two proposals of distributed DNS. We also propose four simple improvements that reduce the traffic generated, and so the power consumption, especially of the most limited, battery powered, devices. We present simulation results that show the impact of our improvements in a typical scenario.